Prostheses for certain joints of the human body, in particular for shoulder joints and hip joints, generally comprise a component designed as a joint socket. In a hip prosthesis, this is usually the component to be fitted into the acetabulum. It can be designed in one piece, or in two pieces with an outer element and a separate support insert to be fitted therein. In the latter design, the problem that arises is that, in the case of cementless implantation, the securing requires the component to be hammered in. This can easily cause damage to the sensitive support insert, particularly if the latter is made of plastic or ceramic material. There is therefore a need for an instrument that facilitates the handling of the joint socket as it is inserted, in particular as it is hammered in.
U.S. Pat. No. 3,589,992 discloses an instrument that has a vacuum-actuated socket holder. At the front end of the elongate shaft, the instrument has a suction head via which a vacuum source can be connected by means of a tubular connection piece with an air valve. The joint socket to be implanted is mounted on the suction head, an underpressure is established in the line leading into the suction head, and the joint socket is in this way held on the suction head. The joint socket can now be inserted and, if appropriate, can be hammered in by way of a strike head arranged at the other end of the shaft. In order to release the instrument, the suction line is ventilated by means of the air valve, as a result of which the vacuum in the suction head ends and the instrument with the suction head can easily be detached from the joint socket that has been hammered in. The connection line is designed separate from the shaft and protrudes in a V-shape from the latter. The instrument is therefore relatively bulky and awkward to handle specifically under the confined operating conditions.
DE-A-197 32 923 discloses an instrument that is further developed. It likewise has a shaft with a suction head at the front end and with a strike head at the rear end. A suction line is also provided which opens out in the suction head and in which an underpressure can be established. However, the underpressure is not provided by attachment of an external vacuum source and is instead generated by a pump integrated in the instrument. For this purpose, a piston pump is provided that is integrated in the shaft. A piston that is displaceable in the longitudinal direction is moved rearward by means of an actuating rod that is pushed transversely through the piston, as a result of which an underpressure is generated by single or repeated actuation. An air valve, in its closed state, ensures that the vacuum does not escape. In this way, as has already been described in detail with regard to the previous instrument, the joint socket can be held securely on the instrument and inserted or hammered in at the intended site. Finally, the air valve is opened, as a result of which the underpressure can escape and the instrument can be easily released from the joint socket. The integrated piston pump represents an improvement over the instrument known from U.S. Pat. No. 3,859,992, but its handling is still relatively complicated. Moreover, apart from the position of the air valve, the user is given no information on whether or not there is sufficient underpressure in the suction line.